This Program Project Grant, Mechanisms of Auditory Dysfunction, consists of interrelated mulitdisciplinary investigations of psychophysical, speech perception, and physiological aspects of auditory dysfunction. The collaborative theme during this renewal is mechanisms of electrical hearing. Subprojects 1 and 2 are concerned with perceptual measures of electrical hearing in human cochlear implant subjects. They will characterize important aspects of intensity and temporal coding in electrical hearing, and relate psychophysical measures of intensity and temporal processing to specific aspects of speech recognition performance obtained in Subproject 3. Subproject 4 examines the physiological correlates of electrically stimulated hearing, the mechanisms by which electrical stimulation excites surviving auditory nerve fibers, and the limitations to psychophysical performance that might be imposed by auditory nerve responses. This program is a multidisciplinary effort involving collaboration among eight investigators, with expertise in auditory physiology, sensory psychology, audiology, phychoacoustics, and otolaryngology. The program, currently in its twenty-third year, makes use of the Program-Project Grant mechanism to achieve scientific collaboration and productivity in a cost effective manner. Research funded by this grant will continue to advance our understanding of the characteristics and mechanisms of hearing and hearing dysfunction and will have direct implications for clinical diagnosis and eventual management of hearing disorders.